With Google Chrome if I read the post, then click the "back" button on the address bar, the post on that page is unread. Not sure if this is the website bug, it it definitely seems wrong

I'd say this is expected behavior. This is what you actually want. Because clicking back button should go to exactly same place where you just were. Without roundtrip through server just loading same cached data, no extra bytes transferred & performance wasted. It should load exactly same data as you just saw. Otherwise it would be confusing going forward & back and seeing data change because page loads from server (new posts appearing or disappearing). If I clicked on something, but from my corner of eye saw something other interesting I wanted to read, I should be able to click back and get exactly that. And not server loading new info and this interesting thing disappearing. If user wants to get newest data on page - that's what Reload/Refresh button is for.